In a conventional high frequency semiconductor device, in order to obtain desired output power, it is necessary to design an exclusive field effect transistor (FET), in which a total gate electrode length is changed, in response to a value of the output power every time when the value concerned is changed.
Moreover, as another method for obtaining the desired output power, a method is adopted, in which FETs with a multi-cell configuration are formed, power supplies are individually prepared for cells of the FETs, when a value of the desired output power is small, some of such FET cells are made not to operate by changing a voltage to be supplied thereto, and when the value of the desired output power is large, a predetermined supply voltage is supplied to all of the FET cells, whereby the value of the desired output power is obtained.
However, in accordance with the conventional method of designing the FET every time when the value of the output power is changed, a mass production effect is not obtained, whereby it is difficult to suppress cost. Moreover, in accordance with the conventional method of changing the supply voltage for each of the FET cells, a plurality of the power supplies must be prepared and individually controlled, and accordingly, a system therefor becomes complicated, and it is difficult to suppress the cost.